1. Field of the Invention
The present invention relates to a magnetic disk cartridge in which a magnetic disk sheet, (which is a magnetic recording medium of very small thickness) is rotatably housed. The invention particularly relates to a magnetic disk cartridge provided with a write-protect member for preventing the erasure of information recorded on a magnetic disk sheet.
2. Background of the Invention
A magnetic disk sheet rotatably housed in a cartridge case has a central circular hole at which a center core is secured. When the drive shaft of a write/read device, which is coupled to the center core, is rotated, the magnetic disk sheet is also rotated. In order to normally write or read magnetically-recorded information into or from the magnetic disk sheet, a writing head or a reading head is moved on the sheet in its radial direction while the sheet is being rotated.
Both a recording/reproduction device and a magnetic disk cartridge are provided with mistaken erasure prevention mechanisms to prevent already-recorded information from being erased by mistake when the cartridge is loaded in the device. These mistaken erasure prevention mechanisms are normally called write-protect mechanisms since they prevent the writing of new information to the disk.
A through hole is provided at one corner of the case of the magnetic disk cartridge to be protected. The recording/reproduction device is provided with a through hole detection means in such a position that the detection means corresponds to the through hole when the cartridge is loaded in the device. The through hole is thus detected by the through hole detection means to make it impossible to write and erase information.
Although the through hole detection means is usually made of either a pin insertable into the through hole or alternatively of a combination of a light emission element which emits light into the through hole and a light reception element which receives the light emitted into the through hole, the detection means is not confined to such structures.
In order to write or erase the information, it is required that the through hole of the case is not detected by the through hole detection means. For that purpose, the case is provided with a write-protect member by which the through hole can be appropriately opened and closed.
FIG. 7 shows a plan view of one corner of a lower half case 1 having a through hole 2. An upper half case 9 has another corresponding positioned through hole. A write-protect shutter 3 is slidably supported to open and close the through hole 2. The lower half case 1 includes a rib 4 for restricting the sliding of the write-protect shutter 3 and projections 5 for putting the shutter 3 in engaged positions respectively exposing and covering the through hole 1.
The write-protect shutter 3 includes a opaque covering portion 6 and legs 7. When the shutter 3 is in the position shown in FIG. 7, the tips of the legs 7 are engaged with the upper projections 5 so that the through hole 2 is opened. At that time, the through hole 2 is detected by a recording/reproduction device so that the device does not erase information. When the write-protect shutter 3 is slide in the direction A so that the tips of the legs 7 are engaged below the second projections 5, the through hole 2 is covered with the covering portion 6 and therefore not detected by the recording/reproduction device, so that the device can erase information.
In order to secure the lower half case 1 and the upper half case 9 to each other, as shown in FIG. 8, the top of a boss 9 provided on the lower half case is secured to the inside surface of the upper half case by ultrasonic fuse-bonding or the like. The diameter of the boss 8 is made slightly smaller than the distance between the legs 7 so that the securing area of the boss 8 and the upper half case 9 is made as large as possible.
Each leg 7 and the boss 8 are located very close to each other as shown in FIG. 8. For that reason, if a material protrusion 10 arises at the joint of the upper half case 9 and the boss 8 due to the securing thereof by the ultrasonic fuse-bonding or the like, the width of the moving passage for the leg 7 is reduced so that the leg slides in contact with the protrusion 10, thus making it impossible to smoothly slide the write-protect shutter 3. If the material protrusion 10 is extremely large, it is impossible to slide the write-protect shutter 3 to open and close the through hole 2. Therefore, the accuracy required to secure the upper half case 9 to the boss 8 needs to be of very high degree.